1. Field of the Invention
Aspects of the present invention draw from the fields of geology, geography, geophysics, applied mathematics, computer science, software engineering, and ergonomics (as it relates to the design of computer interfaces). In particular, the present invention relates to computer-based methods which assist geologists (or others) in constructing, modifying, and testing geologically-consistent model(s) of the subsurface using geographic, well-bore, seismic, and geological analog data, as well as known principles of geology and geophysics.
2. Description of the Prior Art
Geologists are often required to construct models in order to facilitate the efficient extraction of hydrocarbons or minerals from the subsurface, or to control contaminants in subsurface reservoirs. A problem with constructing these models is that subsurface formations are typically either sparsely sampled or sampled at a low resolution, by measurements made in a borehole or by surface geophysical measurements. Also, the measured properties are frequently not those of direct interest to a person attempting to construct a model (e.g., seismic measurements respond to variations in acoustic impedance, whereas the geoscientist may be required to construct a model of the permeability within the subsurface). And, while there exists a large body of knowledge concerning the "interpretation" of well-log, seismic and other geophysical data (see, e.g., O. Serra, Sedimentary Environments from Wireline Logs, Schlumberger Technical Services Publication No. M-081030/SMP-7008 (1985)), the reality is that "interpretation" activities inevitably rely on the judgments of experienced geoscientists.
Thus, it is typically necessary to combine available measurements with geological knowledge (i.e., the knowledge typically possessed by geological "experts") in order to estimate the distribution of the parameters-of-interest in the subsurface. However, this process at least, as currently practiced is complex, cumbersome, and error-prone.
Typically, a geoscientist will attempt to interpret subsurface data on the basis of prior experience. Reasoning, based on analogies to well-characterized subsurface formations or outcrop, he/she will make assumptions about the distribution of geophysical parameters in the formation-of-interest. See, e.g., T. Dreyer, Geometry and Facies of Large-Scale Flow Units in Fluvial-Dominated Fan-Delta-Front Sequences, in M. Ashton (Ed.), Advances in Reservoir Geology, Geological Society Special Publication, 69, 135-174 (1993). When properly applied, this method of reasoning-by-analogy may allow the scientist to predict unknown properties-of-interest based upon available measurement(s) and assumptions about the nature of the formation (e.g., that it resembles the shape of a certain, known formation).
However, in addition to being a time-consuming and dependent upon the availability of appropriate geological "experts," this method of matching to analogue formations suffers from certain problems. In particular, as has been noted in the literature, e.g., I. D. Bryant and S. S. Flint, Quantitative Elastic Reservoir Geological Modeling: Problems and Perspectives, in S. S. Flint and I. D. Bryant (Eds.), Geological Modeling of Hydrocarbon Reservoirs and Outcrop Analogues, International Association of Sedimentologists Special Publication, 15, 3-20 (1993), and J. Alexander, A Discussion on the Use of Analogues for Reservoir Geology, in M. Ashton (Ed.), Advances in Reservoir Geology, Geological Society Special Publication, 69, 175-194 (1993), it is difficult to:
(i) ensure that the selected analogue is appropriate for a given subsurface formation; and
(ii) scale the analogue information to best fit the formation-of-interest.
At present, systematic, rigorous, and efficient methods for scaling the spatial statistics of an "analogue formation" to best match that of a formation- or reservoir-of-interest do not exist. And, even after an initial "analogue" model is created, no systematic, rigorous, and efficient method exists for verifying or testing the model.
A number of prior-art patents address the general topic of geological modeling. U.S. Pat. No. 4,646,240, METHOD AND APPARATUS FOR DETERMINING GEOLOGICAL FACIES, incorporated herein by reference, describes a technique for automatically determining lithological facies from well-log data.
U.S. Pat. No. 5,012,675, INTEGRATING MULTIPLE MAPPING VARIABLES FOR OIL AND GAS EXPLORATION, incorporated herein by reference, describes a technique for integrating geological survey data (e.g., topographic, bathymetric, free air and Bouguer gravity, magnetic, electromagnetic, geochemical, radioactivity, temperature, biotic, geological, and other (non-seismic and non-well-logging) surveys) to locate subsurface features useful for mineral exploration.
U.S. Pat. No. 4,648,268, METHOD OF DEFINING HOMOGENEOUS ROCK FORMATION ZONES ALONG A BOREHOLE ON THE BASIS OF LOGS, incorporated herein by reference, discloses a method for processing well-log data to define formation boundaries along the borehole.
U.S. Pat. No. 4,937,747, ITERATIVE DISJOINT CLUSTER AND DISCRIMINANT FUNCTION PROCESSING OF FORMATION LOG RESPONSES AND OTHER DATA, incorporated herein by reference, details a cluster analysis-based method for computing subsurface rock classifications from well-log data.
U.S. Pat. No. 4,991,095, PROCESS FOR THREE-DIMENSIONAL MATHEMATICAL MODELING OF UNDERGROUND VOLUMES, incorporated herein by reference, describes a technique for subsurface modeling utilizing a regular grid in the longitude-latitude plane and arbitrary resolution in the depth direction.
U.S. Pat. Nos. 5,671,136, PROCESS FOR SEISMIC IMAGING MEASUREMENT AND EVALUATION OF THREE-DIMENSIONAL SUBTERRANEAN COMMON-IMPEDANCE OBJECTS, 5,475,589, SYSTEM FOR EVALUATING SEISMIC SEQUENCE LITHOLOGY AND PROPERTY, AND FOR EVALUATING RISK ASSOCIATED WITH PREDICTING POTENTIAL HYDROCARBON RESERVOIR, SEAL, TRAP OR SOURCE, and 4,679,174, METHOD FOR SEISMIC LITHOLOGIC MODELING, all incorporated herein by reference, describe methods for constructing subsurface images and/or models from seismic data.
U.S. Pat. No. 5,671,344, PROCESS FOR DISPLAYING N DIMENSIONAL DATA IN AN N-1 DIMENSIONAL FORMAT, describes a method for displaying 3-D seismic data on a computer display.
None of these prior-art approaches, either individually or collectively, address the need for an interactive system which enables a skilled geoscientist to effectively create and evaluate multiple, alternative models, comprised of geologically plausible, space-filling objects, while simultaneously viewing relevant portions of a massive database of geographic and geophysical data. The instant invention, as described below, addresses these, and other, needs.